In the treatment of crude oil, it is desirable to dehydrate the crude oil by removing all, or substantially all, of the water mixed with or entrained in the crude oil. Conventionally, the water is removed from the crude oil simply by heating the crude oil in a vessel, such as a storage tank or horizontal pressure vessel, in order to settle the water by gravity out of the crude oil. More recently, apparatus have been developed that simply heat the crude oil, in order to boil the water therein. These apparatus typically result in the undesirable formation of large quantities of a foam comprised of steam bubbles in an oil film. Large quantities of crude oil foam present difficulties with respect to both the heating and processing of the crude oil.
As a result, several apparatuses have been developed in an attempt to treat the crude oil, to remove the water, without causing a substantial amount of foaming. For instance, Canadian Patent No. 1,201,403 issued Mar. 4, 1986 to Murphy Oil Company Limited is directed at an apparatus which includes a heat exchanger, separate from and external to a separation vessel, for preheating the crude oil before it enters the separation vessel. The heat exchanger, which is comprised of a relatively complex glycol heat exchanger, is designed to pre-heat the stream to a temperature which is at least the boiling temperature of water at atmospheric conditions. Thus, two separate devices, being the heat exchanger and the separator, are required. Further, it has been found that the components may not have a satisfactory throughput of crude oil for their relative size and cost. Accordingly, this apparatus may not be particularly cost effective, efficient or desirable for use in treating crude oil.
Reissued Canadian Patent No. 1,302,937 issued Jun. 9, 1992 to Colt Engineering Corporation is directed at an apparatus which includes dehydrator means for receiving the crude oil and producing the dehydrated oil and heater means for maintaining the liquid in the dehydrator means at an elevated distillation temperature such that the dehydrated oil may be produced. The apparatus may further include means for recycling a portion of the dehydrated oil to spray means. The patent states that the spray means are designed to spray the recycled dehydrated oil into the dehydrator means in order to suppress any foam on the surface of the liquid in the dehydrator means. Thus, the primary purpose of the recycling means is foam suppression. However, the patent does indicate that the incoming dehydrated oil is sprayed onto the surface of the liquid in heat exchange contact with the surface of the already heated oil in the dehydrator means. Thus, although this is clearly not the primary purpose, there may be some heat exchange as a result of the recycling means. However, any heating by the recycling means is clearly secondary or supplementary to the heater means only.
Finally, Canadian Patent No. 1,307,489 issued Sep. 15, 1992 to HTI Technology Canada Ltd. is also directed at an apparatus which recycles a portion of the treated oil back through the apparatus. However, the oil is recycled in order to maintain the flow of the oil through the apparatus and so that additional water may be removed from the recycled oil. There is no specific discussion with respect to recycling of the treated oil in order to suppress foam formation or to heat the untreated oil.
There is therefore a need in the industry for a process and an apparatus for treating a crude oil containing water, such that the water is separated therefrom, to produce a treated oil. Further, there is a need for a process and an apparatus which minimize foam formation and treat the crude oil in a relatively energy efficient manner compared to known processes and apparatuses. As well, there is a need for a process and an apparatus which recycle an amount of the treated oil, for mixing with the untreated crude oil, in order that the treated oil heats the untreated crude oil to a temperature such that substantially all the water contained in the crude oil forms a vapour which may be separated from the crude oil. Further, the process and the apparatus preferably recycle the treated oil in a manner such that the treated oil and the untreated crude oil are mixed together to vaporize the water therein prior to the mixture entering a separator for separation of the vapour from the crude oil.